mx=ac/np for n
Cross multiply:
mnpx = ac
Divide each side by mpx:
mnpx/mpx = ac/mpx
Cancel the mpx on the right side:
n = ac/mpx
Cross multiply:
mnpx = ac
Divide each side by mpx:
mnpx/mpx = ac/mpx
Cancel the mpx on the right side:
n = ac/mpx